This invention relates to light detection and ranging apparatus and methods.
Generally, light detection and ranging schemes have been used in the past to derive information relating to the concentration and spacial range, among other things, of particles suspended in air. Such systems have been used to monitor air pollution.
Past systems include a light source which is aimed at particles of interest. A light receiver detects light scattered by such particles and means are provided to derive information relating to the scattered light, e.g., its intensity and/or wavelength. From such parameters, time-varying information relating to particle concentration, type, size, and range, can be determined.
Past apparatus typically use a laser as a light source. In the case where pollution is being monitored, the laser light output is directed toward a portion of the sky, light is scattered by the pollution, and detected by a receiver. Some past apparatus have used a scanner which is basically a rotating mirror that repeatedly sweeps the laser beam, in a plane, about a 360.degree. arc. When a scanner is utilized, the receiver thus detects light scattered from particles in a selected plane.
Such past monitoring permits particle detection only along a selected line or, when a scanner is used, in a selected plane. Such monitoring is impaired when an object, e.g., a hill, tree, building, etc., prevents projection of laser light beyond the object.
It is an object of the present invention to provide a method and apparatus for light ranging and detection for use in the presence of light-blocking objects.
It is a more specific object to provide such a method and apparatus which utilizes only one light source.
In a preferred embodiment of the invention, a plurality of fiberoptic cables are provided adjacent the light output of a laser. When the laser is generating light, the light travels in the cable and provides a light output at the other end, which is located and positioned to monitor a selected portion of the sky. A light receiver is associated with each cable end and serves to detect light backscattered by the ambient pollution. Each receiver is connected to a computer which generates values indicative of different parameters, e.g., particle concentration and spatial range, of each area. The computer is programmed to generate a three-dimensional time-varying map of the volume being mapped.
These and other objects and attendant advantages of the invention will be made apparent in view of the following drawings and detailed description of a preferred embodiment of the invention.